KH isn't very important; it's the GH you want to go by. KH doesn't affect the fish directly, its effect is indirect in that KH stabilises pH, and it's pH that can affect fish.
I'm afraid I don't know the parameters discus need except for soft, acidic water at higher temperature than most tropical fish. Plymouth Discus reckons pH 6.5 for adults but up to 7.0 for babies; GH anything under 10 Gernam degrees (180 ppm) though the author of the article prefers 3 German deg (55 ppm).
